This invention relates to a method for positionally controlling an electric drive and for steering a motor vehicle with a steer-by-wire steering system.
The positions of electric drives must be controlled in a wide variety of technical fields. Examples include not only the electric drives of machine tools and manufacturing robots, but also the valve actuators of steer-by-wire steering systems having hydraulic steering boxes.
All of these positional controls have in common the fact that the position of the electric drive must follow the prescribed setpoint with the least possible delay and without overshooting. It is also desirable that the position control be able to perform effectively with the lowest possible number of sensors, and further, that it exhibit robust control behavior that is insensitive to internal and external disturbances.
The position-control method of the invention is described hereinbelow with reference to the example of a valve actuator of a so-called steer-by-wire steering system having a hydraulic steering box. This does not imply limiting the scope of the instant invention to steer-by-wire steering systems or to methods of steering a motor vehicle with a steer-by-wire system.
Steer-by-wire steering systems are distinguished by the absence of any continuous mechanical connection between the steering wheel and the steered wheels.
There are two sets of problems that must be overcome in the design of steer-by-wire systems. First, the driver's steering input must be transmitted from the steering wheel to the steered wheels, and second, the driver must receive feedback from the steered wheels to the steering wheel. The driver senses this feedback as a torque exerted on him by the steering wheel. This torque will be referred to hereinbelow as the steering feel.
Such a steer-by-wire system must be at least as good as a conventional servo steering system in terms of operational reliability and control behavior. Furthermore, it must be possible to integrate higher-order functions such as tracking control or vehicle dynamics control and crosswind compensation into the steer-by-wire system. Finally, a steer-by-wire system must be readily adaptable to different types of vehicles.
The object of the instant invention is to provide methods for position control, particularly for steering a motor vehicle with a steer-by-wire system, that exhibit high control quality, operate safely and reliably, and permit the integration of higher-order functions.